1. Field of the Invention
The present invention relates to a sheet post-processing apparatus disposed with saddle stitching and folding functions, and in particular to a sheet post-processing apparatus that can realize high-precision folding.
2. Description of the Related Art
Sheet post-processing apparatus disposed with a bookbinding function that binds, with staples, plural sheets on which images have been formed are being developed. As binding methods performed by such sheet post-processing apparatus, there are end stitching, which binds one place or plural places on an edge portion of a sheet bundle, and saddle stitching, which binds plural places in the center portion of a sheet bundle. Among apparatus that perform saddle stitching, there are apparatus disposed with a saddle stitching and folding function that folds the center portion of a bound sheet bundle to form a weekly.
In the saddle stitching and folding function that folds the center portion of a bound sheet bundle to form a weekly, the means for folding the center portion is configured by a blade and a pair of folding rollers. (e.g., JP-A-2005-8418)
In this configuration the means for folding the center portion of the sheet bundle pushes the center portion of the conveyed sheet bundle with the blade into the portion where the pair of folding rollers face each other and folds the sheet bundle with pressure resulting from the rotation of the folding rollers.
The sheet bundle that has been folded is discharged from the folding rollers, conveyed along a conveyance path, and accumulated in a saddle tray.
Because it is necessary for the folding rollers to precisely fold the sheet bundle, it is necessary for the folding rollers to sufficiently impart a predetermined weight with respect to the fold portion of the sheet bundle. For that reason, low-speed rotation is imparted to the folding rollers.
Ordinarily, the folding rollers rotate at a uniform speed, so the folding rollers convey the sheet bundle at the same low-speed rotation as the number of rotations with respect to the fold portion of the sheet bundle with respect also to conveying the sheet bundle after the fold portion of the sheet bundle has been processed. For that reason, the total amount of processing time required to fold the sheet bundle and thereafter convey the sheet bundle requires a lot of time.